SimpleDrawing - Cross Platform

• Allows for the simple drawing of basic shapes on a canvas
• Renders the canvas in a window
• Works on multiple platforms (tested Windows, Linux; should also work on Mac)
• Based on SkiaSharp
  • via Avalonia UI
• User click events are registered

This library is meant for simple applications, so only basic functions are available to keep the API easy to use.

Sample Usage

using Avalonia.Input;
using Avalonia.Media;
using SimpleDrawing;
using SimpleDrawing.Core;

LeoCanvas.Init(Run, 400, 400, clickAction: DrawCircleOnClick);

return;

static async void Run()
{
    try
    {
        LeoCanvas.DrawLine(new(100, 100), new(300, 300));
        LeoCanvas.DrawLine(new(300, 100), new(100, 300), thickness: 4, color: Brushes.Green);
        LeoCanvas.DrawRectangle(new(50, 50), new(100, 80), lineColor: Brushes.Red);
        LeoCanvas.DrawRectangle(new(325, 325), new(375, 375), fillColor: Brushes.Azure);
        LeoCanvas.DrawEllipse(new(200, 300), 50, 75,
                              lineColor: Brushes.Firebrick, fillColor: Brushes.Firebrick);
        LeoCanvas.DrawCircle(new(350, 75), 40, lineThickness: 2.5D,
                             lineColor: Brushes.BlueViolet, fillColor: Brushes.Gold);
        LeoCanvas.DrawText(new(25, 350), "Hello World", 24, Brushes.Lime);

        LeoCanvas.Render();

        LeoCanvas.DrawLine(new(200, 25), new(200, 375), 8);
        LeoCanvas.Render();

        await Task.Delay(TimeSpan.FromSeconds(2));
        LeoCanvas.Clear();
        var x = 50;
        for (var i = 0; i < 10; i++)
        {
            LeoCanvas.DrawLine(new(x, 25), new(x, 375), 8);
            x += 25;
            LeoCanvas.Render();
            await Task.Delay(TimeSpan.FromSeconds(1));
        }

        var imagePath = Path.Combine(Directory.GetCurrentDirectory(), "Data/logo.png");
        LeoCanvas.DrawImageAtLocation(imagePath, new(50, 100), new(350, 175));
        LeoCanvas.Render();

        Console.Write("Press any key to exit...");
        Console.ReadKey();
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
    }
}

static void DrawCircleOnClick(ClickEvent clickEvent)
{
    var radius = clickEvent.Button switch
    {
        MouseButton.Left => 25,
        MouseButton.Right => 50,
        _ => 10
    };
    LeoCanvas.DrawCircle(clickEvent.ClickedPoint, radius);
    LeoCanvas.Render();
}

Main Method

To also support macOS (which requires the UI thread to be the main thread), it is necessary to pass the actual main method to the LeoCanvas.Init method. It will be run in a background thread, hiding most of the complexity from the students, but this method reference is a technical necessity.

Click Events

An Action can be passed to the Init function to register a click handler which will receive the location the user clicked within the canvas as well as information if the left or right mouse button was used.

LeoCanvas.Init(Run, 600, 600, clickAction: DrawCircleOnClick);

static void DrawCircleOnClick(ClickEvent @event)
{
    var radius = @event.Button switch
    {
        MouseButton.Left => 25,
        MouseButton.Right => 50,
        _ => 10
    };
    LeoCanvas.DrawCircle(@event.ClickedPoint, radius);
    LeoCanvas.Render();
}

Rendering Images

Images can be rendered on the canvas using the DrawImageAtLocation function. The image path should be passed as the first parameter and the location as the second parameter.

It is also possible to directly pass an IImage to an overload. Images can be (pre)loaded via the TryLoadImage method to avoid loading them from the disk every time.

This library should support all image formats handled by SkiaSharp (e.g., PNG, JPEG, BMP).

var imagePath = Path.Combine(Directory.GetCurrentDirectory(), "Data/logo.png");
LeoCanvas.DrawImageAtLocation(imagePath, new(50, 100), new (350, 175));

Scale of the images is not checked, make sure to use a proper target rectangle.